When the motorcycle is running at high speed, the grounding load at a front wheel system of a motorcycle decreases due to lift. In the event that a large disturbance is imparted to the front wheel system from a road surface in such a condition, the vibration of the front wheel system increases, thereby damaging the driving stability.
Then, there is provided a proposal in which a steering damper is provided between a steering system member such as a steering bracket and a vehicle body frame for absorbing disturbance from the road surface by virtue of a damping force generated on the steering damper so provided to thereby suppress the vibration of the front wheel system (for example, refer to JP-A-2000-301680).
The steering damper is constructed such that the interior of a cylinder is divided into two oil chambers by a piston which slides in the cylinder as a steering operation takes place, an oil hole (an orifice) is formed in the piston for providing a communication between the two oil chambers, and a bypass passageway is provided for allowing oil in one of the oil chambers to flow into the other oil chamber by bypassing the oil hole, whereby an electromagnetic valve is controlled based on the behaviors of the vehicle which are affected by vehicle speed, steering angle and load which are detected by sensors so that the bypass passageway is closed by the electromagnetic valve so as to increase quickly the damping force to thereby suppress the vibration of the front wheel system.
However, since the conventional steering damper needs sensors for detecting the vehicle speed and steering angle, so that the electromagnetic valve and the like are controlled to operate based on detection signals from the sensors, there are caused problems that the number of components is increased to thereby call for an increase in costs and that highly reliable operations are difficult to be secured due to a delay in control.
The invention was made in view of the problems, and an object thereof is to provide a motorcycle steering damper which requires no electrical control but ensures mechanical operations and which can suppress the vibration of the front wheel system due to disturbance while ensuring the decrease in cost by decreasing the number of components and high reliability.